| Houseflies are insects included in the order Diptera (Gk. | | | | with a series of parallel channels. The fly places the |
| di - two, pteron - wing). Most other orders have two | | | | lobes on the food and secretes saliva through the |
| pairs of wing (i.e. four in all) but houseflies, bluebottles, | | | | channels. The saliva contains enzymes which digest |
| hover flies, mosquitoes, tetse flies, crane flies ('daddy | | | | the food to a liquid which is then pumped back through |
| long legs') etc. have only the single pair. Houseflies are | | | | the proboscis to the gut. |
| of interest principally because they are associated with | | | | Any bacteria in the food accumulate in the proboscis |
| the transmission of certain diseases. | | | | channels and are flushed out with the saliva onto the |
| Apart from the single pair of wings, houseflies share | | | | next substance on which the fly alights. If the first food |
| the typical insect features; their bodies are divided into | | | | sample happens to be human faeces and the next |
| segments which are grouped into a head, thorax and | | | | sample a slice of bread, any bacteria from the faeces |
| abdomen. The thorax carries three pairs of jointed legs | | | | will be transferred to the bread and eaten. If the |
| as well as the wings. There are no appendages on the | | | | bacteria are those which cause intestinal disease, |
| abdomen. | | | | there is the risk that they will cause that disease in the |
| Houseflies lay their eggs in rotting organic matter, with | | | | person who eats the bread. Cholera, typhoid and |
| a preference for stable manure. The eggs hatch into | | | | salmonella food poisoning are diseases that can be |
| white, legless larvae, (maggots), which feed on fluids | | | | spread by houseflies. In addition to the feeding |
| and small particles in the organic waste. As they grow, | | | | mechanism, the bacteria can also be transferred on |
| they shed their skins several times but retain the last | | | | the housefly's legs. |
| one as a hard pupal case in which they undergo the | | | | There are several ways of reducing the spread of |
| drastic changes (metamorphosis) from a maggot to a | | | | disease by houseflies. The most obvious is to store all |
| fully formed housefly. The immature fly pushes its way | | | | food for human consumption in situations which |
| out of the pupal case and allows time for its wings to | | | | houseflies cannot reach. It is also vital to dispose of |
| expand and harden before it flies off. | | | | human waste in such a way that houseflies cannot |
| The housefly poses a health hazard because of its | | | | pick up bacteria from it. This can be achieved by |
| indiscriminate choice of food ranging from human and | | | | modern methods of sanitation and sewage treatment. |
| animal faeces to food awaiting human consumption. | | | | Flies have a range of about one mile so it is best if |
| Houseflies cannot take in solid food. They have a | | | | their potential breeding sites, e.g. manure heaps, are not |
| proboscis which can be extended on to the potential | | | | allowed to accumulate near to urban populations. |
| food. At the end of the proboscis are two flat lobes | | | | |